We intend to characterize a novel epidermal barrier wound response pathway in Drosophila. The . epidermis of both insects and mammals erects a largely impermeable barrier that preventsdehydration, limits injury to soft tissue, and blocks microbial invasion. A major component of this barrier in insects is the cuticular layer, and a major component in mammals is the stratum corneum of the skin. Recent findings from our lab and others indicate that a conservedgenetic pathway, mediated by Grainy head transcription factors, is used in both insects and mammals to regulate the constructionand repair of the epidermal barrier. Thus, we now have the exciting prospect of applying the strengths of Drosophila genetics and molecular biology to the study of epidermal barrier repair in animals. To identify newgenes and molecules in the barrier wound repair pathway, we will perform genetic screens to identify the signaling molecules and receptorsthat inform epidermal cells of their proximity to barrier woundsites. We will also mutagenize barrier wound responsecis-regulatory elements to determine the DNA binding sites required to activate transcription in responseto aseptic wounds,and the factors that act throughthose binding sites. We will perform assays to identify the intracellular signals and biochemical mechanisms that instruct wound pathway transcription factors to activatewound responseenhancers after aseptic injury. A better understanding of this barrier wound repair pathway should improve human health, as the proposed researchwill identify new genes and molecules that can be tested for their influence on epidermal barrier healing in humans. The importance of the human epidermal barrier is documentedby the scoresof tragic and disfiguring human genetic diseases in which the barrier is compromised, by the need for rapid repair of the barrier in the prevention of sepsis and fluid loss in wounded humans, and by the need for properly regulated barrier replacement in the prevention of scarring.